Process and apparatus for the production of diamond

ABSTRACT

The present invention aims at improving a hot filament CVD method and apparatus capable of enlarging the diamond-forming area in relatively easy manner and utilizing effectively the capacity of a thermoelectron radiation material and provides a process and apparatus for producing diamond with excellent productivity as well as a compact size of apparatus, which can be applied to production on a commercial scale. The feature of the present invention consists in subjecting to decomposition, excitation and activation by a thermoelectron radiation material heated at a high temperature a raw material gas comprising at least one carbon source selected from the group consisting of hydrocarbons, hydrocarbons containing oxygens and/or nitrogens in the bonded groups, carbon oxides, halogenated hydrocarbons and solid carbon, hydrogen and optionally any one of inert gases of Group VIII elements, H 2  O, O 2  and F 2  and depositing diamond on the surface of a substrate provided near the thermoelectron radiation material, characterized by surrounding the circumference of the thermoelectron radiation material by a cooling plate, providing a substrate to be deposited with diamond between the cooling plate and the thermoelectron radiation material with small gaps and controlling the surface temperature of the substrate facing the thermoelectron radiation material by the cooling plate and optionally a buffer material inserted between the cooling plate and the substrate, thereby depositing diamond.

TECHNICAL FIELD

This invention relates to an improvement relating to a process for theproduction of diamond by gaseous phase synthesis method and an apparatusfor practicing the same.

TECHNICAL BACKGROUND

In the gaseous phase synthesis of diamond, a number of methods have beendeveloped, for example, a hot filament CVD method comprising utilizing athermoelectron radiation material heated at a high temperature todecompose and activate a raw material gas, a microwave plasma CVD methodcomprising utilizing microwave plasma, a DC plasma CVD method comprisingutilizing DC plasma, a dia-jet method comprising utilizing a DC plasmatorch, a burner method comprising utilizing an oxygen-acetylenecombustion flame, etc. Above all, the hot filament CVD method and themicrowave plasma CVD method are typical methods.

According to the hot filament CVD method comprising utilizing athermoelectron radiation material heated at a high temperature todecompose and activate a raw material gas, it is possible to enlarge acoating zone by designing the shape of a filament more readily than inthe other plasma utilizing process. Even if the thermoelectron radiationmaterial, as an exciting source, is enlarged, however, the ordinaryapparatus construction is so composed that a substrate is arranged onone plane to face the thermoelectronic emission material and theutilization efficiency of the space relative to the thermoelectronradiation material is low so that the diamond-forming area is markedlylimited relatively to the capacity of the exciting source. Since thesize of the thermoelectron radiation material is generally smallerrelatively to the size of a reaction vessel and diamond is formed onlyin the vicinity of the thermoelectron radiation material, the dead zonein a reaction vessel is large and the diamond-forming area is smallrelatively to the occupied area of the apparatus, so that the apparatusis not suitable for use as a production apparatus on a commercial scale.The flow of a raw material gas is governed by convection and is notsimple near the thermoelectron radiation material because of using areaction pressure of several ten to several hundred Torr andaccordingly, effective feeding of the raw material gas and exhausting ofthe reacted gas cannot well be carried out.

In the hot filament CVD method, therefore, it has eagerly been desiredto develop a process for the synthesis of diamond and an apparatus forpracticing this process, wherein a large sized thermoelectron radiationmaterial is provided as an exciting source and a substrate is arrangedwith a high space efficiency relatively to the thermoelectron radiationmaterial, so that the capacity of the exciting source can be displayedto the maximum, the utility efficiency of a raw material gas in areaction zone can be increased, the dead zone in a reaction vessel canbe decreased and the occupied area of the synthesis apparatus can bereduced per the diamond-forming area, thus obtaining excellentproductivity with a compact size of apparatus. The present invention hasbeen made so as to respond to the desirement.

In various synthesis techniques of diamond, the inventors have madevarious studies to improve the hot filament CVD method and apparatuscapable of enlarging the diamond-forming area in relatively easy mannerand to utilize effectively the capacity of a thermoelectron radiationmaterial, and consequently, have reached a process and apparatus forproducing diamond with excellent productivity as well as a compact sizeof apparatus, which can be applied to production on a commercial scale.The present invention can thus be accomplished.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention provides a process for the productionof diamond comprising subjecting to decomposition, excitation andactivation by a thermoelectron radiation material heated at a hightemperature a raw material gas comprising at least one carbon sourceselected from the group consisting of hydrocarbons, hydrocarbonscontaining oxygens and/or nitrogens in the bonded groups, carbon oxides,halogenated hydrocarbons and solid carbon, hydrogen and optionally anyone of inert gases of Group VIII elements, H₂ O, O₂ and F₂ anddepositing diamond on the surface of a substrate provided near thethermoelectron radiation material, characterized by surrounding thecircumference of the thermoelectron radiation material by a coolingplate, providing a substrate to be deposited with diamond between thecooling plate and the thermoelectron radiation material with small gapsand controlling the surface temperature of the substrate facing thethermoelectron radiation material by the cooling plate and optionally abuffer material inserted between the cooling plate and the substrate,thereby depositing diamond, and an apparatus for practicing the process.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 (a), (b) and (c) are schematic views of one embodiment of thepresent invention.

FIG. 2 (a), (b), (c) and (d) are schematic views of another embodimentof the present invention.

FIG. 3 (a) and (b) are schematic views of a further embodiment of thepresent invention.

FIG. 4 is a side view of the same embodiment as that of FIG. 3.

FIG. 5 is a schematic view of a further embodiment of the presentinvention.

FIG. 6 (a) and (b) are schematic views of a further embodiment of thepresent invention.

FIG. 7 is a schematic view of one embodiment of the present invention,in which a plurality of filaments under tension are arranged to form asame plane.

BEST EMBODIMENT FOR PRACTICING THE INVENTION

As a particularly preferable embodiment of the present invention, thereare a process and apparatus for the production of diamond, as describedabove, in which a wire rod consisting of a high melting point metal,carbon fiber or carbon rod is used as the above described thermoelectronradiation material, a plurality of the thermoelectron radiationmaterials are vertically stretched in a same plane to form a plane ofthe thermoelectron radiation materials, cooling plates having substratesto be deposited with diamond, fitted to both the sides thereof, areprovided to put the plane of the thermoelectron radiation materialsbetween the cooling plates, the inside of a reaction vessel is soconstructed that the above described raw material gas is allowed to flowonly in the gap between the two cooling plates substantially facing toeach other, and the raw material gas is equally fed to the gap betweenthe faced cooling plates from the lower part of the reaction vessel andexhausted from the upper part.

In another embodiment of the present invention, a raw material gas isblown off against the thermoelectron radiation materials from aplurality of gas feed ports fitted to a cooling plate or buffermaterial, and when another raw material gas is simultaneously fed fromthe lower part of the reaction vessel, the other raw material gas havinga same or different composition is blown off.

In the present invention, the distance between the above describedthermoelectron radiation materials and the surface of a substrate to bedeposited with diamond is preferably 40 mm or less, and in order todeposit diamond while controlling the distance between the abovedescribed thermoelectron radiation materials and the surface of thesubstrate to be deposited with diamond correspondingly to the thicknessof diamond formed on the surface of the substrate, it is preferable toprovide an apparatus having a mechanism for moving a buffer material orcooling plate fitted with the substrate.

In the present invention, diamond can be deposited by the use of anapparatus comprising such a constructive element that a plane formed ofthe thermoelectron radiation materials is put in between cooling plateseach being provided with a substrate to be deposited with diamond, and aplurality of the constructive elements are provided in a reactionvessel.

In a particularly preferable embodiment of the present invention,furthermore, diamond is deposited by using an apparatus comprising ameans for forming DC plasma between the thermoelectron radiationmaterials as a hot cathode and a substrate fitted to the buffer materialor cooling plate.

The feature of the present invention will now be illustrated.

Substrates are arranged in the vicinity of thermoelectron radiationmaterials to put the thermoelectron radiation materials between thesubstrates from both the sides thereof, which are surrounded by coolingplates, the gaps between the substrates facing each other and thethermoelectron radiation materials are relatively narrow and a rawmaterial gas is substantially flowed through the gaps to cause reactionthereof, whereby diamond is deposited at both the sides of thethermoelectron radiation materials. Thus, the productivity can more beincreased as compared with the prior art in which the deposition iscarried out only at one side.

A buffer material can be fitted to the cooling plate and a substrate canbe fitted to the cooling plate directly or via a buffer material (whichwill hereinafter be referred to as "substrate-supporting cooling plate"sometimes).

Since the reaction is carried out in the gap formed by the substrate andthermoelectron radiation materials and decreased, particularlypreferably to at most 40 mm, and the diamond synthesis conditions can berealized by controlling the surface temperature of the substrate by thecooling plate and optionally the buffer material, the thermoelectronradiation materials can effectively be utilized over a wide range, notin part as usual.

Depending on the shape of the thermoelectron radiation material, amethod of surrounding the circumference thereof by substrate-fittedcooling plates is varied, but when using a wire-shaped high meltingpoint metal, carbon fiber or carbon rod as the thermoelectron radiationmaterial, it is rendered possible to surround the circumference of thethermoelectron radiation materials with a large area by the substrate tobe deposited with diamond in effective manner and to largely increasethe productivity by vertically stretching a plurality of thethermoelectron radiation materials to form a plane of the thermoelectronradiation materials and arranging the cooling plates provided withsubstrates to be deposited with diamond at both the sides of the planeto put the plane between them. Furthermore, the synthesis conditions ofthe substrates, arranged at both the sides of the thermoelectronradiation materials, can readily be rendered equal to largely increasethe productivity.

Furthermore, the internal structure of a reaction vessel is soconstructed that a raw material gas is flowed only through the gapbetween two cooling plates or substrate-fitted cooling plates, arrangedto substantially face each other and to put the plane formed of thethermoelectron radiation materials between the cooling plates from boththe sides thereof, and the raw material gas is equally fed to the gapbetween the faced cooling plates from the lower part of the reactionvessel and exhausted from the upper part thereof. Thus, the dead zone ofthe reaction vessel can markedly be reduced to give a compact synthesisapparatus and the flow of the raw material gas is rendered uniform fromthe lower part to the upper part of the reaction vessel to giveeffective utilization of the raw material gas.

In addition to the construction described above, blow-off holes areprovided on the cooling plate or where necessary on the substrate-fixedsurface and a carbon source gas or a mixed gas of a carbon source gaswith hydrogen is blown off against the thermoelectron radiationmaterials from the blow-off holes, whereby more uniform formation ofdiamond is rendered possible on the substrates provided at the upper andlower part of the substrate-supported cooling plate verticallymaintained and the synthesis speed of diamond can also be increased.

Provision of a plurality of construction elements for putting the planeformed of the above described thermoelectron radiation materials inbetween the substrate-supported cooling plates, etc. from both the sidesof the plane in a reaction vessel results in remarkable increase of thetotal quantity of diamond-forming areas by a compact installation.

On the other hand, the inventors have proposed a process for thesynthesis of diamond as disclosed in Japanese Patent Laid-OpenPublication No. 52699/1989, wherein a DC voltage is applied tothermoelectron radiation materials connected to a negative pole and asubstrate to be deposited with diamond, connected to a positive pole,and DC plasma is formed between the thermoelectron radiation materialsand the substrate, whereby to utilize thermal activation by thethermoelectron radiation materials and plasma activation by the DCplasma.

In the present invention, using, as a hot cathode, a plane formed ofthermoelectron radiation materials and using, as an anode, anelectroconductive buffer material inserted in between a substrate and acooling plate, or a substrate-fitted cooling plate surrounding the planefrom both the sides thereof, a DC voltage is applied thereto to form DCplasma between them. Thus, it is found that the synthesis rate ofdiamond can markedly be increased by applying a DC power of at least 50W/cm³ per unit area of a space surrounded by substrates provided to faceeach other at a pressure of more than 50 Torr.

In an installation constructed of a plurality of the above describedconstruction elements in a reaction vessel, it is also possible tosimultaneously increase both the growth rate of diamond and the totalquantity of diamond-forming areas and to largely increase the quantityof diamond formed by using, as a cathode, thermoelectron radiationmaterials and using, as an anode, a substrate or a substrate-supportedcooling plate and if necessary, an electroconductive buffer materialinserted in between the cooling plate and the substrate, applying a DCvoltage thereto and thereby forming DC plasma between the thermoelectronradiation materials and the substrate.

In the present invention, the distance between the thermoelectronradiation materials and the surface of the substrate is preferably atmost 40 mm. When the distance is small, there arises such a problem thatif diamond is grown thick during synthesis thereof, the distance betweenthe thermoelectron radiation materials and the surface of the substrateget smaller and consequently, the synthesis temperature rises at thegrowth front of diamond to change the synthesis conditions when otherconditions are same, resulting in deterioration of the quality of theresulting diamond.

This problem can be solved by providing a mechanism for moving thesubstrate-supported cooling plate correspondingly to growth of diamondso as to maintain the distance between the thermoelectron radiationmaterials and the surface of the substrate at a predetermined value, andcontrolling the cooling capacity of the cooling plate. Thus, thickdiamond can be obtained under substantially the same conditions.

According to the present invention, in the hot filament CVD method,thermoelectron radiation materials can be large-sized and a substratecan be arranged at a space position with a high efficiency to thethermoelectron radiation materials as an exciting source, where DCplasma is formed between the thermoelectron radiation materials andsubstrate. Thus, the space capacity of the exciting source can beexhibited at the maximum of efficiency and the exciting capacity fordecomposing and activating a raw material gas can markedly be improved.Accordingly, there can be provided a process and apparatus for thesynthesis of diamond, which are excellent in productivity and in whichthe utility efficiency of a raw material gas is high in the reactionzone, the dead zone in a reaction vessel is small, the occupied area ofthe synthesis apparatus per diamond-forming area is small and both thediamond-forming area and synthesis rate of diamond are large with acompact apparatus.

The present invention will now be illustrated with reference to theaccompanying drawings in detail.

FIG. 1 to FIG. 6 are schematic views of various embodiments forpracticing the present invention, in which the same numerals have thesame meanings.

Referring to FIG. 1, (a) is a front view of the apparatus, (b) is a planview thereof and (c) is a side view thereof, in which 1 designates areaction vessel and 2 designates viewing windows arranged at the rightand left sides.

A raw material gas comprising at least one carbon source ofhydrocarbons, hydrocarbons containing oxygen and/or nitrogen in bondinggroups thereof, carbon oxides, halogenated hydrocarbons and solidcarbon, hydrogen and if necessary, inert gases and any one of H₂ O, O₂and F₂ is introduced from a gas inlet 4 at the lower part of thereaction vessel 1 and divided to be uniformly distributed in thereaction vessel. The reacted gas is exhausted upwards from a divided gasexhaust port 3 to uniformly exhaust the gas. Substrate-supported coolingplates 5, provided at the front side and rear side, can be moved backand forth. 6 designates tray-cum-buffer materials for supporting asubstrate 7 provided at the front side and rear side, which function asa means for both fixing the substrate 7 and controlling the coolingcapacity and which are fitted to the substrate-supporting cooling plate5 after providing with the substrate 7. 8 designates cooling plates atthe left and right sides and 9 designates cooling plates at the upperand lower parts, which are fitted to the interior wall of the reactionvessel to surround the thermoelectron radiation materials from left andright and from upper and lower. The substrate-supporting cooling plates5 are arranged in such a manner that the gaps from the cooling plates 8and 9 are maintained as smaller as possible in order to prevent from gasflowing during reaction in the space between the substrate-supportingcooling plates 5 and the internal wall of the reaction vessel.

Thermoelectron radiation materials 10 are constructed of a large areaplane of thermoelectron radiation materials obtained by giving a tensionto linear thermoelectron radiation materials (high melting point wirerods, carbon fibers), for example, using a weight, thereby drawing themto maintain the linear shape and stretching them to form a planeconsisting of a number of the thermoelectron radiation materials. Eachwire rod of the thermoelectron radiation materials 10 is connected toelectrodes at the upper and lower parts (not shown).

FIG. 2 is a schematic view of another embodiment for practicing thepresent invention, in which (a) is a perspective view of the partscorresponding to 5, 6 and 7 of FIG. 1, the substrate-supported coolingplate 5, the tray-cum-buffer material 6 for supporting the substrate andthe substrate 7. (b), (c) and (d) of FIG. 2 are respectively a sideview, a view from the substrate-fitted surface and a base view of thetray-cum-buffer material for supporting the substrate. 16 gas blow-offholes 11 are provided and substrates 7 are arranged not to clog theblow-off holes 11. 13 designates a raw material gas feed port to thetray-cum-buffer material for supporting the substrate and 12 designatesa groove made, as a gas flow passage, on the contact surface with acooling plate of the tray-cum-buffer material for supporting thesubstrate. The depth of the groove 12 is so controlled that a gas isuniformly blown off from the gas blow-off holes 11 (not shown).

The substrate-supporting cooling plate 5 and the tray-cum-buffermaterial 6 for supporting the substrate are firmly fixed without gap, sothat no gas is substantially leaked except from the blow-off holes. Thesubstrate 7 is tightly fixed to the tray-cum-buffer material 6 forsupporting the substrate by a fixing means to decrease thermalresistance at the contact boundary as less as possible (not shown).

The method of feeding a gas from the substrate-fitted surface shown inFIG. 2 is not always applied to both the substrate-fitted surfaces facedeach other, but when applied to only one side, a large substrate can bearranged since the holes on the one side are not clogged. When a gas isfed from both the substrate-fitted surfaces facing each other, it isdesired that the position of blow-off holes on one side and that ofblow-off holes on the other side are shifted somewhat each other so asto blow off the gas uniformly against thermoelectron radiationmaterials.

FIG. 3 and FIG. 4 are schematic views of a further embodiment of thepresent invention for practicing the present invention, FIG. 3 (a) beinga plan view and (b) being a front view, and FIG. 4 being a side view.This apparatus comprises 4 sets of construction elements in a reactionvessel, the one construction element being so constructed thatfundamentally, the both sides of a plane formed of the thermoelectronradiation materials 10 is put in between the cooling plates 5 forsupporting the substrates 7.

Feeding of a raw material gas to a reaction vessel 1 is carried out byfeeding hydrogen or hydrogen and a carbon source gas and optionally aninert gas of Group VIII element of Periodic Table to a gap between thesubstrate-supporting cooling plates 51 and 52 supporting the substratesfacing each other at both the sides of a plane formed of thethermoelectron radiation materials 10 from a nozzle-like raw materialgas feed port 4. In addition, a carbon source gas or a mixed gas of acarbon source gas and hydrogen is fed through a gas feed conduit 14 to araw material gas feed port 13 to the tray-cum-buffer material 6 forsupporting the substrate and then blown off against the thermoelectronradiation materials 10 from a plurality of gas blow-off holes 11,provided on the substrate-supported surface. In FIG. 3, a raw materialgas is fed to each reaction space through a common circuit, but it isalso possible to supply raw material gases differing in composition tothe reaction spaces by providing independent feed circuits everyreaction spaces. In this case, diamonds can simultaneously besynthesized under different synthesis conditions in one reaction vessel.

These raw material gases are exhausted upwards from the gas exhaust port3 provided to be divided to uniformly exhaust the reacted gas in theupper part of each of the reaction spaces. 15 designates a main exhaustport for evacuating the whole of the reaction vessel in high vacuumtogether with the gas exhaust port 3.

The cooling plates 51 and 52 for supporting the substrates can be movedback and forth against the plane formed of the thermoelectron radiationmaterials. Correspondingly to growth of diamond, thesubstrate-supporting cooling plates can be moved to maintain thedistance between the thermoelectron radiation materials and thesubstrate surface at a predetermined value. The tray-cum-buffer material6 for supporting the substrate has both functions of fixing thesubstrate 7 and controlling the cooling capacity and after providing thesubstrate, it is tightly fixed to the substrate-supporting cooling plate51 or 52 in such a manner that the thermal resistance at the contactboundary is maintained as little as possible. The cooling plates 8 and 9are respectively provided to surround the substrate-supporting coolingplates 51 and 52. The substrate-supporting cooling plates 51 and 52should preferably be arranged with a gap from the cooling plates 8 and9, which is rendered as narrow as possible so that gas flow is notcaused in the space between the cooling plates 51 and 52 and the innerwall of the reaction vessel during reaction.

The thermoelectron radiation materials 10 are similar to those of FIG. 1and have a power source for heating the thermoelectron radiationmaterials 10 in each of the construction elements (not shown). As theheating power source, there can be used one common power source orrespectively independent power sources. In this case, the temperature ofthe thermoelectron radiation materials can be varied in each of theconstruction elements and diamond can simultaneously be synthesizedunder different synthesis conditions in one reaction vessel, thusobtaining diamond differing in quality.

The reaction vessel 1 is constructed of a box-type vessel 21 and a baseplate 22. When a substrate is charged or discharged before or after thereaction, the box-type vessel 21 is held up and taken away, then acooling jacket 19 composing an upper cover is taken away andsubsequently, cooling plates 20 in front and rear are removed. Then, thesubstrate 7 is taken away from the substrate-supporting cooling plates51 and 52 together with the tray-cum-buffer material 6 for supportingthe substrate. Means for supporting the thermoelectronic emissionmaterials 10 is of a cassette type, so exchange of the thermoelectronradiation materials can be done by exchanging a cassette carrying them.The substrate 7 can be set by operation in the reverse order thereto.

FIG. 5 is a schematic view of a further embodiment for practicing thepresent invention. This embodiment corresponds to the construction ofFIG. 1 (c) to which a DC power source 16 is added by connecting thecathode to the thermoelectron radiation materials 10 and the anode tothe tray-cum-buffer material 6 for supporting the substrate, throughcurrent feed terminals 17. After heating the thermoelectron radiationmaterials at a high temperature, a DC voltage is applied using thethermoelectron radiation materials 10 as a hot cathode to form DC plasma18 mainly between the thermoelectron radiation materials 10 andsubstrate 7.

FIG. 6 is a schematic view of a still further embodiment for practicingthe present invention, (a) being a plan view and (b) being a side view.In this embodiment, there are provided 4 sets of construction elementsin a reaction vessel, each of the construction elements beingconstructed of a plane formed of the thermoelectron radiation materials10 put in between the substrate-supporting cooling plates 5, as in thecase of FIG. 3. Since both the surfaces of the cooling plate 5 forsupporting the substrate 7 can be utilized, the construction of thisembodiment is more simple and compact than that of FIG. 3. In this case,however, when the cooling plate 5 for supporting the substrate 7 ismoved during synthesis, the distance from the thermoelectron radiationmaterials 10 is varied inside and outside and accordingly, thesubstrate-supporting cooling plate 5 is not moved during synthesis, ingeneral.

A DC power source (not shown) is also provided as in the case of FIG. 5,while a cathode is connected to the thermoelectron radiation materials10 and an anode is connected to the tray-cum-buffer material 6 forsupporting the substrate, followed by applying a DC voltage to form DCplasma 18.

Each of the construction elements has a power source (not shown) forheating the thermoelectron radiation materials. These heating powersources and DC power sources can use one power source in common or canrespectively have independent power sources in the constructionelements. When using an independent power source in each of theconstruction elements, the temperature of the thermoelectron radiationmaterials and DC plasma conditions can be changed and diamond can thusbe synthesized under different synthesis conditions in one reactionvessel, thereby obtaining once diamond with different qualities.

The present invention relates to gaseous synthesis of diamond by the hotfilament CVD method or by that jointly using DC plasma. The raw materialgas used in the present invention includes a carbon source and hydrogenas essential components. Examples of the carbon source are hydrocarbonssuch as CH₄, C₂ H₂, C₅ H₈, etc., hydrocarbons containing oxygen inbonding groups, such as CH₃ OH, C₂ H₅ OH, (CH₃)₂ CO, etc., hydrocarbonscontaining oxygen and nitrogen in bonding groups, such as CH₃ NO, etc.,hydrocarbons containing nitrogen in bonding groups, such as (CH₃)₂ NH,etc., carbon oxides such as CO₂, CO, etc., halogenated hydrocarbons suchas CF₄, CH₃ F, etc. and the like. As occasion demands, at least one ofinert gases, for example, Group VIII elementary gases of Periodic Table,such as Ar, He, Xe, etc. and H₂ O, oxygen and F₂ can be added. Thecomposition of the raw material gas is not particularly limited, but itis desired that carbon atoms in the carbon source gas are present in aproportion of at most 10% to hydrogen atoms and oxygen atoms are presentin a proportion of at most 35% to carbon atoms.

The pressure in the reaction chamber is generally in the range of 1 to760 Torr, the temperature of the thermoelectron radiation materials isgenerally in the range of 1600° to 2600° C. and the temperature of thesubstrate surface is generally in the range of 400° to 1200° C.

In the hot filament CVD method, raw material gases are decomposed andactivated by thermoelectron radiation materials heated at a hightemperature. Since active species are mainly transported by diffusion ingaseous phase, synthesis of diamond can fundamentally be carried out inall directions round the surface of the thermoelectron radiationmaterial, as a center, if the temperature of the substrate surface is ina correct range. The concentration of the active species becomes higherthe nearer they approach the thermoelectron radiation materials andbecomes lower the farther they part therefrom.

The distance between the thermoelectron radiation materials andsubstrate surface is varied depending upon the temperature of thethermoelectron radiation materials, the surface thereof, the pressure ofthe reaction system, the raw material gases, etc., but it is requiredthat the distance is within a range of at most 40 mm, preferably at most30 mm, since if larger than 40 mm, the diamond growth rate becomessmaller than 0.5 μm/hr and no practical diamond growth rate can beobtained. The lower limit of the gap between them is 1 mm.

It is closely related with the shape of the thermoelectron radiationmaterial how to enlarge the area of surrounding the thermoelectronradiation material so as to obtain a large diamond forming area. As theshape of a thermoelectron radiation material with a large area, aplate-like two-dimensional shape or coil-like three-dimensional shapeare taken into consideration. However, a thermoelectron radiationmaterial with a three-dimensional shape or constructedthree-dimensionally is not suitable so as to satisfy the requirementsthat the circumference of the thermoelectron radiation material issurrounded by substrates at a same distance from the surface of thethermoelectronic emission material and the distance is preciselycontrolled. On the contrary, in the two-dimensional plane-likethermoelectron radiation material according to the present invention,substrates can be arranged to put the thermoelectron radiation materialbetween the substrates from both the sides, so that the circumference ofthe thermoelectron radiation material is surrounded with a very highefficiency and the distance between the thermoelectron radiationmaterials and the substrate surface can readily be controlled.

As the thermoelectron radiation material, there can be used a large areathermoelectron radiation material obtained by imparting a tension tolinear thermoelectron radiation materials to draw and maintain a linearshape and stretching them to form a same plane of a number of wires, asdisclosed in Japanese Patent Laid-Open Publication No. 72992/1989, whichthe inventors have proposed as to enlargement of two-dimensionalthermoelectron radiation materials. FIG. 6 shows an example in the caseof imparting a tension, for example, by a weight according to thismethod. In the present invention, this large-sized thermoelectronradiation material is used and put in between substrates facing eachother, so that the circumference of the thermoelectron radiationmaterial is surrounded by the substrates in high efficiency. As thethermoelectron radiation material of the present invention, for example,wire rods of high melting point metals such as W, Ta, Re, etc. or carbonfibers can be used. Furthermore, carbon rods with a high temperaturestrength are formed in a plane and used as a thermoelectron radiationmaterial.

In this construction, substrates facing each other are preferablysubjected to same synthesis conditions. There is a difference between acase where a plane containing thermoelectron radiation materials ishorizontal and a case where it is vertical. Where a plane containingthermoelectron radiation materials is horizontally arranged, a substratepositioned above the thermoelectron radiation materials is at a highertemperature, due to the effect of convection, than that positioned belowthem, and the gas flow is different between on the upper substrate andon the lower substrate. On the other hand, where the plane containingthermoelectron radiation materials is vertically arranged, thesubstrates facing each other are substantially subjected to samesynthesis conditions.

In the vertical construction, in particular, a raw material gas can moresmoothly be passed through a reaction zone by providing a reactionvessel having such a construction that a raw material gas is flowedthrough only the gap between two cooling plates substantially facingeach other, whereby the raw material gas is uniformly fed from the lowerpart of the reaction vessel to the gap between the cooling plates facingeach other and exhausted from the upper part of the reaction vessel.Since the gas is not fed to other parts than the reaction zone, thereaction gas is used for the reaction effectively. As one example forrealizing this embodiment, it is only required that the end of a coolingsupporting base, to which a substrate is to be fitted, is fixed to theinner wall of the reaction vessel or the cooling jacket surrounding thesame without substantial gap.

In the present invention, a plurality of gas feed ports can be fitted tothe substrate-supporting cooling plate or optionally to the buffermaterial inserted in between the cooling plate and substrate and acarbon source gas or a mixed gas of a carbon source gas and hydrogen gascan be blown off from the blow-off holes opened on the surface to whichthe substrate is fixed against the thermoelectron radiation materials.This blowing-off can fully be appropriated for feeding of the rawmaterial gas or can jointly be used with the feeding of the raw materialgas from the lower part of the reaction vessel as described above. Thus,it is rendered possible to more uniformly form diamond on the substratesprovided at the upper part and lower part of the cooling plate forsupporting the substrates vertically, and moreover, the synthesis rateof diamond can also be improved.

This is probably due to that when the raw material gas is only fed fromthe lower part of the reaction vessel to the gap of thesubstrate-supporting plates, the raw material gases fed differ incomposition between at the lower part where the unreacted gas is firstfed and at the upper part where the reacted gas by the thermoelectronradiation materials is then fed.

Since in the present invention, an unreacted raw material gas with thesame composition can directly and uniformly be supplied from the gasblow-off holes arranged uniformly on the substrate-fixed surface againstthe thermoelectron radiation materials, uniform synthesis of diamond inthe vertical direction is considered to be possible.

Furthermore, it is not always required that the raw material gas fed tothe gaps of substrate-supporting cooling plates from the lower part ofthe reaction vessel and the raw material gas fed from the gas blow-offholes arranged on the substrate-fixed surface are the same in gaseouscomposition, but rather, the quality of diamond can be controlled bypositively changing the gaseous compositions.

For example, high quality diamond with a less content of non-diamondcarbon can be synthesized at a high rate by feeding a raw material gascontaining no carbon source gas to the gaps of the cooling plates fromthe lower part of the reaction vessel, or by decreasing the proportionof carbon atoms to hydrogen atoms in the raw material gas to at most 4%and adjusting the proportion of carbon atoms to hydrogen atoms in theraw material gas fed from the blow-off holes arranged on thesubstrate-fixed surface to at most 10%, larger than in the raw materialgas fed to the gaps of the cooling plates from the lower part of thereaction vessel.

On the other hand, when one construction element is constructed of anelement comprising substrate-supporting cooling plates holding a planeformed of the thermoelectron radiation materials from both the sidesthereof and a plurality of the construction elements are set in areaction vessel, installation parts such as reaction vessel, evacuationsystem, gas supplying system, etc. can jointly be used. As a result, theinstallation can be very compacted and the installation cost can bereduced. When at least one of the raw material gas feed systems, powersources for heating the thermoelectron radiation materials and DC powersources is rendered independent in each of the construction elements,diamond can readily be synthesized under different synthesis conditions,thus obtaining different quality diamonds simultaneously.

As a means for increasing the excitation capacity of a raw material gasof thermoelectron radiation materials, it is considered to raise thetemperature of the thermoelectron radiation materials or to increase thesurface area thereof, for example, by increasing the number of wires orincreasing the size of wires. In order to improve the homogeneity of theexcitation source, it is preferable to densely stretch linear filaments.

In order to further improve the excitation capacity of an excitationsource, the inventors have proposed a method, as disclosed in JapanesePatent Laid-Open Publication No. 52699/1989, which comprises connectingthermoelectron radiation materials to cathode, connecting adiamond-coated substrate to anode, applying a DC voltage thereto to formDC plasma between the thermoelectron radiation materials and substratesand thereby jointly using thermal activation by the thermoelectronradiation materials and plasma activation by the DC plasma. In thepresent invention, using a plane formed of thermoelectron radiationmaterials as a hot cathode and using a substrate to be deposited withdiamond, surrounding the plane from both the sides thereof,substrate-supporting cooling plates or optionally an electroconductivebuffer material inserted in between the cooling plate and substrate asan anode, applying a DC voltage thereto and thereby forming DC plasmabetween them. When plasma is formed by the electrode constructionaccording to the present invention, such a large advantage can beobtained that uniform plasma is formed between the electrodes with alarge area.

In the present invention, a cathode surface is provided in such a mannerthat gas is freely passed through the central part of a pair of anodesurfaces arranged to face each other, unlike in the ordinary plasmaformation of parallel plane system in which a set of a cathode surfaceand anode surface are faced each other and plasma is formed in a spaceheld between them, and accordingly, the one cathode surface caneffectively be utilized, so that plasma be formed in a space with a sizeof two times as large as the space of the prior art.

The electric power for forming DC plasma is at least 50 W/cm³ and thepressure is in the range of about 50 to 500 Torr.

In any case, since when the excitation capacity of a raw material gas ofthe excitation source is desired to be improved, the calorific value ismarkedly increased, it is necessary to cool the substrate so as tomaintain the temperature of the substrate surface at 400° to 1200° C.,preferably 700° to 1200° C. corresponding to the diamond formingtemperature by the ordinary gaseous phase synthesis method.

In the present invention, therefore, a substrate to be deposited withdiamond is fitted to a cooling plate and cooled. Thus, the cooling platemust have a sufficiently cooling capacity. When the cooling capacity ofthe cooling plate is too high to maintain the temperature of thesubstrate surface within the above described temperature range capableof synthesizing diamond even by controlling the flow rate or temperatureof cooling water, it is desirable to insert a buffer material with a lowthermal conductivity in between the cooling plate and substrate and tosuppress the cooling capacity, thereby controlling the temperature ofthe substrate surface. Furthermore, the cooling plate should have alarge area sufficient to cover the thermoelectron radiation materialsand to cut off the heat from the thermoelectron radiation materials.

As the material of the cooling plate in the present invention, there arepreferably used materials having high cooling capacity, for example,water-cooled copper jackets, water-cooled stainless steel jackets andcopper plates or stainless steel plates with which water-cooled pipesare tightly contacted.

A substrate is directly fitted to a cooling plate or fitted to a coolingplate after fixed to the above described buffer material. During thesame time, the fixing must be carried out in such a manner that thermalcontact is sufficiently given effect to smoothly conduct heatconduction. Exchange of the substrate can more effectively be carriedout by using the buffer material as a tray for fixing the substrate,fitting the substrate thereto outside a reaction vessel and then fixingto the cooling plate, rather than by directly fixing the substrate tothe cooling plate. When using a material having a high heat conductivityas the buffer material, this system can be appropriated in a case whereit is desired to increase the cooling capacity.

As the buffer material as described above, there can be used materialshaving high heat conductivity, such as Mo, W, WC-Co, Si, AlN, etc., andmaterials having low heat conductivity, such as SiO₂, etc.

When DC plasma is formed, the use of the buffer material as an anodeleads to requirement of selecting a material having electroconductivityat a temperature when it is used.

The material used as the substrate of the present invention includeshigh melting point metals of forming carbide, i.e. Group VA and VIAmetals of Periodic Table and Si, carbides, nitrides and carbonitrides ofGroup VA and VIA metals of Periodic Table and Si, ceramics obtained bysintering at least one of these carbides, nitrides and carbonitrideswith binder materials and carbon substrates having intermediate layersof the above described materials formed.

When DC plasma is formed, it is similarly required to select a materialhaving electroconductivity at the diamond synthesis temperature for thesubstrate. Above all, Si, SiC, Si₃ N₄, Mo, W and carbon substrateshaving an intermediate layer of Si, vapor deposited, are particularlypreferable. When using SiC in the case of appropriating DC plasma,doping of Al or N is required, and when using a sintered compact of Si₃N₄, it is required to add TiN, thereby imparting electroconductivity.

In the present invention, the distance between the thermoelectronradiation materials and the substrate surface is very important and thethermoelectron radiation materials are held from both the sides thereofby the cooling plates which are respectively independent and have afunction of controlling the distance from the thermoelectron radiationmaterials. In the apparatus shown in FIG. 3, however, the cooling plates51 and 52 may respectively be moved as a group interlocked closely.

A further advantage of the present invention consists in that theapparatus of the present invention has such a structure that coolingplates each having high cooling capacity surround and enclosethermoelectron radiation materials and the thermoelectron radiationmaterials having large area can thus be used, so that a large electricpower be applied. As to DC plasma, a DC plasma with a high energydensity can be formed at a high voltage by applying a large electricpower.

Such thermoelectron radiation materials and DC plasma have very highdecomposing and activating capacity of a raw material gas. In addition,a raw material gas is fed to only the gap between substratessubstantially arranged to face each other and to put filaments inbetween them, so that the reaction efficiency can largely be increased.Consequently, synthesis of diamond with high quality is renderedpossible at a high speed, i.e. several tens μm/hr over a forming zone ofa large area.

EXAMPLE 1

Using an apparatus substantially shown in FIG. 1, gaseous synthesis ofdiamond was carried out. A reaction vessel was very compact as having aninner size of □50 cm×15 cm. As the thermoelectron radiation material, 50tungsten wires each having a diameter of 0.3 mm and a length of 25 cm,stretched vertically in a same plane, were used. The intervals of thefilaments were varied at the end parts and central part in such a mannerthat the filaments were stretched to be dense at the end parts and to besparse at the central part and the temperature distribution is thusdecreased at the central part and end parts. When the 50 filaments werestretched, their lateral width was 25 cm. As a cooling plate, there wasused a water-cooled jacket whose inner reinforcement was sufficientlymade by ferrite type stainless steel. As substrates to be deposited withdiamond, 32 polycrystal silicon substrates each having a size of 50mm×50 mm×3 mm t were used and the 4 substrates were laterally arrangedin one level on a substrate-supporting tray-cum-buffer material,followed by repeating this arrangement on 4 steps. A surface of apolycrystalline silicon substrate was subjected to a mirror polishingand then to a scratching treatment with diamond powder of NO. 5000. Asthe tray-cum-buffer material which, after fixing the substrates, wasfixed to the cooling plate, a Mo plate with a thickness of 25 mm wasused.

As a raw material gas, hydrogen containing 3% by volume of ethanol wasused and introduced into the reaction vessel at a flow rate of 6liter/min. The pressure in the reaction vessel was adjusted to 200 Torr.The filament temperature was adjusted to 2150° C. and the distancebetween the filament and substrate was controlled, so that thetemperature of the substrate surface be 950° C. At that time, thedistance was 6 mm. Measurement of the surface temperature was carriedout by making a hole in the Mo plate used as a tray, followed by passinga sheath thermocouple through the hole, further making a hole in thesilicon substrate, followed by passing a thermocouple through the hole,and measuring the temperature in close vicinity of the surface. Underthis condition, the system was maintained for 10 hours to effectsynthesis of diamond.

Consequently, diamond with an average thickness of 100 μm could besynthesized at a growth speed of 10 μm/hr. At the same time, the area ofthe formed diamond was 800 cm² corresponding to a diamond synthesisquantity much larger than that of the prior art apparatus.

The resulting diamond had a very high quality substantially free fromamorphous carbon, as represented by the results of Raman spectroscopicanalysis that the ratio of the peak height of amorphous carbon and thepeak height of diamond was at most 0.05. Furthermore, the full width athalf maximum of peak of diamond was 5.5 inverse centimeter, near that ofhigh purity single crystal.

EXAMPLE 2

Using the same apparatus as that of Example 1, i.e. the same reactionvessel, cooling paltes and filaments, and using the tray-cum-buffermaterial as shown in FIG. 2 (a) to (d), gaseous phase synthesis ofdiamond was carried out.

As a substrate to be deposited with diamond, there was used apolycrystalline silicon substrate of 50 mm×50 mm×3 mm t, same as that ofExample 1, which was subjected to mirror polishing of the surfacethereof and then to a scratching treatment with diamond powder of No.5000. The 4 substrates were laterally arranged in one level on asubstrate-supporting tray-cum-buffer material, followed by repeatingthis arrangement on 4 steps, and the substrate and tray were tightlyfixed to reduce thermal resistance. As the substrate-supportingtray-cum-buffer material, a Mo plate with a thickness of 25 mm was used.As a raw material gas to be fed to the gap between thesubstrate-supporting cooling plates from the lower part of the reactionvessel, hydrogen gas containing 1% by volume of ethanol was flowed at aflow rate of 4.5 liter/min, while as a raw material gas to be fed fromblow-off holes arranged on the substrate-fixed surface, hydrogen gascontaining 4% by volume of ethanol was flowed at a flow rate of 0.75liter/min from one substrate-fixed surface, amounting to a sum of 1.5liter/min. In the similar manner to Example 1, synthesis of diamond wascarried out by adjusting the pressure in the reaction vessel to 200Torr, the filament temperature to 2150° C. and the distance between thefilaments and substrate surface to 6 mm, controlling the coolingcapacity of the cooling plates to adjust the temperature of thesubstrate surface to 980° C. and maintaining these conditions for 10hours.

Thus, diamond with a mean thickness of 150 μm was fast synthesized at agrowth speed of 15 μm/hr. The quality of the resulting diamond wascomparable to that of Example 1. In Example 1, diamonds synthesized atthe uppermost steps and lowermost steps of the substrate-supportingtray-cum-buffer material were different in film thickness and the filmthickness at the uppermost steps was larger by 15% than that at thelowermost step. On the contrary, in this Example, the thicknessdifference was suppressed to about 5%.

Diamond could uniformly be synthesized with an improved growth speed inthe diamond-forming zone by jointly applying a method of feeding a rawmaterial gas from the blow-off holes arranged on the substrate-fixedsurface.

EXAMPLE 3

Using substantially the same apparatus as shown in FIG. 3 and FIG. 4,gaseous synthesis of diamond was carried out. The apparatus was acompact installation including a reaction vessel with an inner dimensionof 80 cm width, 65 cm height and 55 cm depth. As the thermoelectronradiation materials, there were used 50 tungsten wires of 0.5 mm indiameter and 30 cm in length, vertically stretched in a same plane insuch a manner that the filament gaps are varied at the end parts andcentral part, i.e. stretched densely at the end parts and sparsely atthe central part so as to reduce the temperature distribution betweenthe central part and end parts. When 50 filaments were stretched, thelateral width was 25 cm.

As a cooling plate, there was used a water-cooled jacket whose innerreinforcement was sufficiently made by ferrite type stainless steel. Assubstrates to be deposited with diamond, polycrystalline siliconsubstrates each having a size of □50 mm×5 mm t were used. A surface of apolycrystalline silicon substrate was subjected to a mirror polishingand then to a scratching treatment with diamond powder of NO. 5000. The4 substrates were laterally arranged in one level on asubstrate-supporting tray-cum-buffer material, followed by repeatingthis arrangement on 4 steps, and tightly fixed so as to reduce thethermal resistance between the substrate and tray. As thesubstrate-supporting tray-cum-buffer material, a Mo plate with athickness of 15 mm was used. One construction element is constructed ofan element comprising substrate-supporting cooling plates holding aplane formed of the thermoelectron radiation materials from both thesides thereof. In each of the construction elements, as a raw materialgas to be fed to the gap between the substrate-supporting cooling platesfrom the lower part of the reaction vessel, hydrogen gas containing 1%by volume of ethanol was flowed at a flow rate of 5 liter/min was used,while as a raw material gas to be fed from the blow-off holes arrangedon the substrate-fixed surface, hydrogen gas containing 4% by volume ofethanol was flowed at a flow rate of 1 liter/min, amounting to a sum of2 liter/min, from one substrate-fixed surface. Synthesis of diamond wascarried out by adjusting the pressure in the reaction vessel to 250Torr, the filament temperature to 2200° C. and the distance between thefilaments and substrate surface to 5 mm, controlling the coolingcapacity of the cooling plates to adjust the temperature of thesubstrate surface to 1000° C. and maintaining these conditions for 20hours.

Thus, diamond with a mean thickness of 400 μm was fast synthesized at agrowth speed of 20 μm/hr. The quality of the resulting diamond wascomparable to that of Example 1 or 2. The formed diamond had an area of3200 cm² which was much larger than that formed by the prior artapparatus and furthermore, showed a film thickness distribution within arange of at most 5% in the diamond forming zone and good quality hardlydiffering therein.

EXAMPLE 4

Using substantially the same apparatus as shown in FIG. 6, gaseoussynthesis of diamond was carried out. The apparatus was a compactinstallation including a reaction vessel with an inner dimension of 70cm width, 60 cm height and 50 cm depth. As the thermoelectron radiationmaterials, there were used 44 tungsten wires of 0.5 mm in diameter and20 cm in length, vertically stretched in a same plane in such a mannerthat the filament gaps are varied at the end parts and central part,i.e. stretched densely at the end parts and sparsely at the central partso as to reduce the temperature distribution between the central partand end parts. When 44 filaments were stretched, the lateral width was20 cm.

As a cooling plate, there was used a water-cooled jacket whose innerreinforcement was sufficiently made by a copper alloy. As substrates tobe deposited with diamond, low resistance silicon substrates each havinga size of □150 mm×10 mm t were used. The surface of the substrate wassubjected to a mirror polishing to a scratching treatment with diamondpowder of NO. 5000 and then to a roundness treatment of the ridgelinesforming the diamond so that DC plasma be not concentrated. One substratewas fitted and tightly fixed to a substrate-supporting tray-cum-buffermaterial to reduce the thermal resistance between the substrate andtray. As the substrate-supporting tray-cum-buffer material, a Mo platewith a thickness of 10 mm was used.

One construction element is constructed of an element comprisingsubstrate-supporting cooling plates holding a plane formed of thethermoelectron radiation materials from both the sides thereof. In eachof the construction elements, hydrogen gas containing 4% by volume ofmethane was fed at a flow rate of 5 liter/min from the lower part of thereaction vessel to the gap between the cooling plates. Synthesis ofdiamond was carried out by adjusting the pressure in the reaction vesselto 180 Torr, the filament temperature to 2250° C. and the distancebetween the filaments and substrate surface to 5 mm, applying a DC powerof 120 W/cm³ per unit volume of the space formed between the substratesfacing each other, controlling the cooling capacity of the coolingplates to adjust the temperature of the substrate surface to 980° C. andmaintaining these conditions for 10 hours.

Thus, diamond with a mean thickness of 350 μm was fast synthesized at agrowth speed of 35 μm/hr. The quality of the resulting diamond wassomewhat inferior to that of Example 1, 2 or 3 according to assessmentof the Raman spectroscopic analysis method in respect of completeness ofdiamond, i.e. that the peak strength of diamond was slightly weak andthe full width at half maximum was widened. This is probably due to thatthe diamond is contaminated with W and the internal stress is large.Above all, the problem of the contamination with W can be solved by theuse of high purity carbon as the thermoelectron radiation material.Since both the forming area and the forming rate of diamond are largeaccording to this method, the production quantity of diamond can more beincreased as compared with the prior art.

It will clearly be understood from these examples that according to thepresent invention, high quality diamond can be synthesized at a highspeed over a wide forming zone in a very compact synthesis apparatus andaccordingly, the present invention serves to reduction of the productioncost by gaseous phase synthesis method of diamond.

UTILITY AND POSSIBILITY

According to the present invention, there can be provided an apparatusfor the synthesis of diamond, which is compact and excellent inproductivity and which comprises large-sized thermoelectron radiationmaterials used as an excitation source in a hot filament CVD method anda reaction vessel in which substrates are arranged with such a highefficiency in a space for the thermoelectronic emission materials thatthe space capacity of the excitation source can be exhibited to themaximum, the utility efficiency of a raw material gas can be increasedin a reaction zone and the dead zone of the reaction vessel can bedecreased to reduce the occupied area of the synthesis apparatus per thediamond forming area.

Since in the apparatus of the present invention, a large electric powercan be applied to the thermoelectron radiation materials with a largesurface area and a large electric power can be applied at a relativelyhigh pressure to form a DC plasma with a high energy density, thedecomposition and activation capacity of a raw material gas can berendered very high. In addition, a raw material gas is fed to only thegap between the substrates substantially facing each other to holdfilaments between them, so the reaction efficiency can be rendered veryhigh.

Since one construction element is constructed of an element comprisingsubstrates faced each other to hold filaments between them in a reactionvessel, and a plurality of the construction elements are installed, adiamond-forming zone with a large area can be obtained in a compactapparatus and consequently, high quality diamond can be synthesized overthe diamond-forming zone with a large area at a high speed, e.g. severaltens μm/hr.

We claim:
 1. A process for the production of diamond comprisingsubjecting to decomposition, excitation and activation, by athermoelectron radiation material heated at a high temperature, a rawmaterial gas comprising at least one carbon source selected from thegroup consisting of hydrocarbons, hydrocarbons containing oxygens and/ornitrogens in the bonded groups, carbon oxides, halogenated hydrocarbonsand solid carbon, hydrogen and optionally any one of inert gases ofGroup VIII elements, H₂ O, O₂ and F₂ and depositing diamond on thesurface of a substrate provided near the thermoelectron radiationmaterial, characterized by surrounding the circumference of thethermoelectron radiation material by a cooling plate, providing asubstrate to be deposited with diamond between the cooling plate and thethermoelectron radiation material such that a small gap exists betweenthe substrate and the thermoelectron radiation material and controllingthe surface temperature of the substrate facing the thermoelectronradiation material by the cooling plate and optionally a buffer materialinserted between the cooling plate and the substrate, thereby depositingdiamond.
 2. The process for the production of diamond, as claimed inclaim 1, in which a wire rod consisting of a high melting point metal,carbon fiber or carbon rod is used as the above described thermoelectronradiation material, a plurality of the thermoelectron radiationmaterials are vertically stretched in a same plane to form a plane ofthe thermoelectron radiation materials, cooling plates having substratesto be deposited with diamond, fitted to both the sides thereof, areprovided to put the plane of the thermoelectron radiation materialsbetween the cooling plates, the inside of a reaction vessel is soconstructed that the above described raw material gas is allowed to flowonly in the gap between said cooling plates substantially facing to eachother, and the raw material gas is equally fed to the gap between thefaced cooling plates from the lower part of the reaction vessel andexhausted from the upper part.
 3. The process for the production ofdiamond, as claimed in claim 1 or 2, in which a raw material gas isblown off against the thermoelectron radiation materials from aplurality of gas feed ports fitted to a cooling plate or buffermaterial, and when another raw material gas is simultaneously fed fromthe lower part of the reaction vessel, the other raw material gas havinga same or different composition is blown off.
 4. The process for theproduction of diamond, as claimed in claims 1 or 2, in which thedistance between the above described thermoelectron radiation materialsand the surface of a substrate to be deposited with diamond is at most40 mm.
 5. The process for the production of diamond, as claimed inclaims 1 or 2, in which diamond is deposited while controlling thedistance between the thermoelectron radiation materials and the surfaceof the substrate to be deposited with diamond correspondingly to thethickness of diamond formed on the surface of the substrate.
 6. Theprocess for the production of diamond, as claimed in claims 1 or 2, inwhich one constructive element is constructed of a plane formed of thethermoelectron radiation materials, put in between cooling plates eachbeing provided with a substrate to be deposited with diamond, and aplurality of the constructive elements are provided in a reactionvessel, thereby depositing diamond.
 7. The process for the production ofdiamond, as claimed in claims 1 or 2, in which diamond is depositedwhile forming DC plasma between the thermoelectron radiation materialsand a substrate fitted to the buffer material or cooling plate.
 8. Anapparatus for the production of diamond in which a raw material gascomprising at least one carbon source selected from the group consistingof hydrocarbons, hydrocarbons containing oxygens and/or nitrogens in thebonded groups, carbon oxides, halogenated hydrocarbons and solid carbon,hydrogen and optionally any one of the inert gases of Group VIIIelements, H₂ O, O₂ and F₂ is subjected to decomposition, excitation andactivation by a thermoelectron radiation material heated at a hightemperature and diamond is deposited on the surface of a substrateprovided near the thermoelectron radiation material, characterized inthat the circumference of the thermoelectron radiation material issurrounded by a cooling plate, a substrate to be deposited with diamondis provided between the cooling plate and the thermoelectron radiationmaterial such that a small gap exists between the substrate and thethermoelectron radiation material and the surface temperature of thesubstrate facing the thermoelectron radiation material is controlled bythe cooling plate and optionally a buffer material inserted between thecooling plate and the substrate, thereby depositing diamond.
 9. Theapparatus for the production of diamond, as claimed in claim 8, in whicha wire rod consisting of a high melting point metal, carbon fiber orcarbon rod is used as the above described thermoelectron radiationmaterial, a plurality of the thermoelectron radiation materials arevertically stretched in a same plane to form a plane of thethermoelectron radiation materials, cooling plates having substrates tobe deposited with diamond, fitted to both the sides thereof, areprovided to put the plane of the thermoelectron radiation materialsbetween the cooling plates, the inside of a reaction vessel is soconstructed that the above described raw material gas is allowed to flowonly in the gap between said cooling plates substantially facing to eachother, and the raw material gas is equally fed to the gap between thefaced cooling plates from the lower part of the reaction vessel andexhausted from the upper part.
 10. The apparatus for the production ofdiamond, as claimed in claim 8 or 9, in which the cooling plate orbuffer material has a plurality of raw material gas feeding ports forblowing off a raw material gas against the thermoelectron radiationmaterial.
 11. The apparatus for the production of diamond, as claimed inclaims 8 or 9, in which the distance between the above describedthermoelectron radiation materials and the surface of a substrate to bedeposited with diamond is at most 40 mm.
 12. The apparatus for theproduction of diamond, as claimed in claims 8 or 9, in which a mechanismfor moving the cooling plates each being fitted with the substrates isprovided to control the distance between the thermoelectron radiationmaterials and the surface of a substrate to be deposited with diamond.13. The apparatus for the production of diamond, as claimed in claims 8or 9, in which a plurality of constructive elements constructed of aplane formed of the thermoelectron radiation materials, put in betweencooling plates each being provided with a substrate to be deposited withdiamond, are provided in a reaction vessel.
 14. The apparatus for theproduction of diamond, as claimed in claims 8 or 9, in which a means forforming DC plasma between the thermoelectron radiation materials as ahot cathode and cooling plates or buffer materials fitted withsubstrates to be deposited with diamond, as an anode, is provided.